The invention relates to a method or an apparatus for controlling the draft of a fiber mixture (e.g. of a sliver) of a textile machine, with means being provided to detect the fluctuations in mass of the fiber mixture which is supplied to the drafting arrangement. A changeable drafting zone compensates the fluctuations in mass and is provided with a delay time in order to take into account the running time of the fiber mixture from the measuring means to a control application point.
Prior literature (xe2x80x9cFeedback control systems in modern sizing machinesxe2x80x9d by Prof. Burgholzxe2x80x94Textilpraxis 1963, July, p. 643) shows a drafting arrangement in which fluctuations in the mass of fiber material supplied to the drafting arrangement are detected by way of a measuring element. The movement of the measuring roller which is produced by the fluctuations in mass is stored via a mechanical storage element and is transmitted in a time-delayed manner to a mechanical device for influencing the draft quantity. A time delay for the control intervention is thus achieved in a mechanical manner, which intervention takes the distance between the measuring place and the actual control application point for the evening of the fiber mixture into account.
In newer devices, as have been described in DE-A1-36 19 248 for example, this intermediate storage of the signal of the measuring element is performed electronically. This cited publication states further that the time of delay is corrected according to the magnitude and type of the measured fluctuation in the mass, which means that as soon as the signal of the measured fluctuations in mass is located outside of the normal fluctuations of mass, the draft intervention will occur earlier. This reduces the distance between the control application point and the measuring location of the measuring element. This device allows in particular an improved compensation of sudden fluctuations in the mass of a sliver.
EPA-A2-803 596 further proposes an apparatus and method for the direct determination of set-points for the control application point of a draw frame. Several measured values of a quality-characterizing value such as the CV value are used in order to determine the optimized parameter, such as the control application point in a test run. This optimized control application point is to remain substantially unchanged during the operation. This method, which uses the CV value, leads to disadvantages particularly when the textile machine which is situated upstream of the drafting arrangement is supplied with only one untwisted sliver which shows relatively large fluctuations in mass.
An apparatus is further known from EP-A1 533 483, with influencing quantities which influence the measured signal of the measuring member being detected by a fuzzy logic control device and being linked to a knowledge base. A corrective value for the measured signal is produced therefrom. The delivery speed of the fiber material supplied by the drafting arrangement can be used as an influencing quantity for example. This means that the corrective value relates to the respective design of the determined measured value on the basis of influencing quantities and not to the determination of the control application point. For the purpose of correcting the control application point, it is proposed in this embodiment that a signal analysis is performed at the drafting arrangement output on the basis of the analysis of the response signal of the measuring element, thus enabling the performance of respective interventions. This means that a correction of the control application point will only be performed at a time when the flaw in the fiber material has already passed through the drafting arrangement and thus can no longer be corrected. Moreover, a further measuring element is required at the output of the drafting arrangement, as well as a complex fuzzy logic control device.
A device shown in DE-A1 42 15 682 in which a correction of the control application point is performed according to a specific method. The method for the correction of the control application point is only started when there is a transient signal in the measuring element before the drafting arrangement which exceeds a predetermined tolerance value. With the help of the response signal which is detected by a measuring element at the output of the drafting arrangement, a respective intervention is performed via the control unit comparison with the transient signal in order to correct the control application point. This system is not continuously in operation and additionally requires a measuring element at the output of the drafting arrangement. Moreover, a correction of the control application point is only performed when the sliver containing the flaw has already left the drafting arrangement.
Examinations have shown that the evenness of the formed sliver, or the CV value and the spectrogram image, changes once the fiber material is supplied to the draw frame at different delivery speeds. This means that one has noticed that the control application point between the two pairs of drafting rollers changes in its position depending on the delivery speed. This fact is usually not disadvantageous in xe2x80x9cpure draw framesxe2x80x9d, because these machines are usually operated with substantially constant speeds.
This fact is usually not disadvantageous in xe2x80x9cpure draw framesxe2x80x9d, because these machines are usually operated with substantially constant speeds.
If such a drafting arrangement unit is arranged downstream of a carding machine for further processing of the card sliver, major delivery fluctuations in the drafting arrangement must be expected as a result of the operating procedure in the carding machine. These delivery fluctuations in the carding machine are caused by changes in production, running down the machine during changes of the cans, running in new clothings, and other circumstances. As a result of this frequent change of the delivery speeds, there is also a displacement of the control application point with respect to the measuring place before the drafting arrangement. This leads to maintaining an adverse sliver quality in respect to sliver regularity (CV value) and the spectrogram image.
This fact is also not considered, or only partly with limitations, by the apparatuses mentioned in connection with the state of the art.
Various devices are further known from the state of the art, e.g. from EP-A1176 661, with the regulation of an autoleveller draw frame begin performed on the basis of inlet and outlet measuring element in conjunction with a predetermined setpoint value. In the exhibited example, the signal for influencing the control parameters which is measured at the output is used for overall amplification and the runtime of the controlling electronic system. This device is to be used in particular to correct abrupt changes in the supplied fiber mass. This device relates to the matching of the control parameters during the drafting process and not to any principal setting of the control intensity or calibration of the drafting arrangement.
Insofar as such drafting arrangement operates autonomously as a draw frame, it was common practice up until now to make respective settings of the control parameters on the draw frame by sliver tests which were performed in a stationary manner in the laboratory. The determined fluctuations in mass were determined in comparison with a predetermined setpoint value (sample sliver) and respective interventions in the control parameters on the drafting arrangement were made. The stopping and renewed start-up of the draw frame to perform such tests and for setting the draw frame did not have any major influence on the productivity or efficiency of the unit.
As soon as this drafting arrangement is operated in direct connection with an upstream textile machine (e.g. a carding machine), such sliver tests performed in the lab are not easily possible without reducing the overall efficiency of the entire system. This means that as soon as the sliver tests are performed in a stationary manner in the laboratory, it is also necessary to stop the textile machine which is upstream of the drafting arrangement during these tests. When the textile machine concerns a carding machine, it is relatively problematic to put this machine with its relatively large moved masses back into operation again. This means that the efficiency of the system decreases.
A device is further known from DE-A1196 15 947 in which a function is determined on the basis of several CV values whose minimum leads to an optimized parameter such as a control application point or amplification for the control of the draw frame or the carding machine. The optimized parameter is determined in a pre-operational test or setting run of the draw frame or carding machine and maintained during operation in a substantially unchanged way.
It is now an object of the present invention to provide a method and an apparatus for setting the drafting arrangement in order to perform optimized control interventions by considering maintaining a high efficiency of the entire plant, particularly when a textile machine is provided directly upstream of the drafting arrangement for the purpose of supplying fiber material. Additional objects and advantages of the invention will be set forth in the following description, or may be obvious from the description, or may be learned through practice of the invention.
This object is achieved on the one hand in such a way that, for changing certain control parameters, the delivery speed (LG) of the fiber mixture (7) and/or the comparison between the measured course of the mass of the fiber material (Fi) supplied by the drafting arrangement with a predetermined setpoint course of the mass (setpoint) is/are used.
The term xe2x80x9cdelivery speedxe2x80x9d relates to the speed of the fiber material which is supplied to the drafting arrangement. The measuring element for detecting the fluctuations in mass is located before the entrance to the drafting arrangement as seen in the direction of conveyance.
This device allows that the control intervention is performed at an optimal time, or in an optimized magnitude, in order to completely compensate any fluctuation in mass as determined by the measuring element.
The drafting arrangement could be provided with merely one drafting zone (single-zone drafting arrangement) or with several drafting zones (e.g. preliminary draft and main draft).
It is preferably proposed that the position of the control application point to the measuring element is corrected depending on the delivery speed of the fiber mixture.
It is further proposed that the change in the position of the control application point is performed on the basis of a curve as predetermined by the control unit. This curve was produced first manually on the basis of experimental values and test results and was used by the control unit to determine a corrective value. The curve is determined on the basis of the values (distance of the control application point to the measuring place) and the delivery speed of the fiber material supplied to the drafting arrangement.
If a machine (e.g. a carding machine) is provided upstream of the drafting arrangement which supplies the produced fiber material (e.g. the sliver) to the downstream draw frame, it is advantageous to integrate this curve in the control unit of said upstream machine in order to determine the correction of the position of the control application point. This is advantageous because the delivery speed of the supplied fiber material is known to said machine or its control unit or has already been determined there.
It is further proposed that the distance of the control application point from the measuring element is reduced with rising delivery speed.
For the purpose of considering different fiber materials, it is proposed that several curves can be selected in the control unit according to the selected fiber material. Depending on the fiber feed (staple, mixture, etc.), the drafting characteristics change in the drafting characteristics change in the drafting arrangement and thus also the position of the control application point.
In order to avoid unnecessarily burdening the regulating device in case of minor fluctuations of the delivery speed, it is proposed that the change in the position of the control application point is only performed when the delivery speed of the fiber mixture leaves a predetermined tolerance threshold.
It is further proposed that when comparing the measured course of the mass of the fiber material as supplied by the drafting arrangement with a predetermined setpoint course of the mass (setpoint), the deviations which exceed the tolerance value are used for changing the control parameters.
The setting of the control intensity is to be understood as the control parameter in particular, which intensity characterizes a value by which the draft is changed into a setpoint mass on the basis of a measured differential signal of the output mass (mean value of the supplied fiber mass). The intervention made on the drafting quantity is to be dimensioned in such a way that the actual value is brought back to the setpoint value.
It is preferably further proposed that the course of the mass is depicted in the form of a spectrogram which is compared with a standard spectrogram which is predetermined to the control unit. The xe2x80x9ctermxe2x80x9d compared shall be understood in such a way that the determined spectrogram is placed in the control unit by a control program (software) over the standard spectrogram, with the deviations determined from the contour of the standard spectrogram being determined and evaluated via a respective electronic evaluation system. This evaluation device can be used in particular to determine any occurring xe2x80x9cpeaksxe2x80x9d and/or xe2x80x9cchimneysxe2x80x9d of the actual spectrogram as compared with the standard spectrogram. These evaluations can be used to take measures manually or automatically following the evaluation of the respective progress of the contour of the spectrogram in order to change the control parameters or settings in such a way that on the one hand the determined xe2x80x9cpeaks and or chimneysxe2x80x9d are avoided and on the other hand the contour of the actual spectrogram approaches the contour of the standard spectrogram or is brought close to a matching. A tolerance field can be provided which allows upward and downward deviations from the course of the standard spectrogram without performing any interventions in the control parameters (e.g. the position of the control application point). This prevents any xe2x80x9cbuild-up processxe2x80x9d of the control system.
The measures for changing the control parameters can comprise the following: adjustment of the control intensity, i.e. the determination of the magnitude of the change in draft on the basis of a determined differential signal between actual and setpoint value (mean value of fiber mass); displacement of the control application point to the one or other side; increase of the pressing pressures of the drafting rollers; and change of the drafting distance and further measures. The choice of the measure is made on the basis of the evaluation. The control can be based on a catalog of measures (expert system).
The measures for changing the control parameters can comprise the following: Adjustment of the control intensity, i.e. the determination of the magnitude of the change in draft on the basis of a determined differential signal between actual and setpoint value (mean value of fiber mass), displacement of the control application point to the one or other side, increase of the pressing pressures of the drafting rollers, change of the drafting distance and further measures. The choice of the measure is made on the basis of the evaluation. The control can be based on a catalog of measures (expert system).
Preferably, the spectrogram deviations will be used in the range of between 5 and 150 cm period lengths for the measuring process. It is possible with this device to perform purposeful optimizations of the control device without requiring any running down of the upstream textile machine (carding machine) and with simultaneously compensating internal tolerances within the control device.
A method is further proposed in which the course of the mass is depicted as a mean value which is compared with a predetermined setpoint value. In particular, this device allows an optimal setting of the control intensity, so that the fluctuations in mass which deviate from the setpoint mean value are returned completely to said value.
Measures for the correction of the control devices can be a displacement of a control application point to either the one or the other side, or the adjusting quantity of the draft on the basis of a determined differential signal between an actual and a setpoint value.
In order to calibrate the effectiveness of the control device with respect to any upward or downward deviation from the setpoint mean value, it is proposed that for setting the control parameters the fiber mass supplied to the drafting arrangement is changed per measuring interval. This means that for an evaluation process, the drafting arrangement unit is supplied with an increased fiber mass and with a lower fiber mass for a further measuring process. An error in the mass is intentionally produced in this method by the machine (or apparatus) upstream of the drafting arrangement unit in order to check, or possibly correct, the effectiveness of the control intensity.
In addition to the evaluation of the spectrogram with respect to the standard spectrogram, the determined coefficient of variation (CV value) can be used which is compared with a predetermined CV value of the setpoint course of the mass. The length CV value can be used with a length of cut of between 20 cm and 3 m.
In order to correct the deviation in the mass (occurring peaks in mass), the displacement of the control application point can be used.
Preferably, the fiber mixture is supplied by a carding machine of the drafting arrangement unit.
To ensure that the adjustment of the control parameters also meets the needs of the conditions during the working operation, it is proposed that during the run-up of the carding machine a warm-up period is set during which certain monitorings performed by the control unit are ceased. This also relates to such monitorings which measure the course of the mass of the fiber mixture in the drafting arrangement. This means that an adjustment of the control parameters can only be performed following the expiration of the warm-up function. In the cold state, the working units via which and between which the fiber material is conveyed has different processing characteristics which correspond not necessarily to the conditions during operation. Cold rollers can have the tendency for example to extract fibers from fiber material. This could lead to fluctuations in the mass, however, which are caused merely by the system per se. That is why the calibration of the control devices should be performed under operating conditions, i.e. after the completion of the warm-up phase. After the completion of this phase, a length counter can be activated which is provided to supply information about the production. The material produced during the warm-up phase can be deposited in a separate can. This separately stored material can be returned to the blowroom for reprocessing.
An apparatus according to the invention may be provided with means by which the position of the control application point to the measuring element is determined on the basis of the delivery speed of the fiber mixture.
The invention is further solved by an apparatus, with means being provided with which the position of the control application point to the measuring element is determined on the basis of the delivery speed of the fiber mixture.
These means are preferably formed by a control device, in particular a microcomputer, which causes the initiation of the change in the draft on the basis of data deposited and stored in the control device in conjunction with signals which are transmitted to the control device by a measuring element for the detection of the delivery speed of the fiber material.
It is further proposed that the fiber material is supplied from a carding machine to a downstream drafting arrangement unit. The control unit of the carding machine is provided with means in order to transmit a corrective signal to determine the position of the control application point of the downstream drafting arrangement to the control unit of the drafting arrangement to initiate the change in the draft.
An apparatus of the invention may have at least one further means provided in order to detect the course of the mass of the fiber material as supplied by the drafting arrangement unit. The signals of the means are transmitted to the control unit which determines the deviations on the basis of a predetermined setpoint value and produces control signals according to the deviations in order to change certain control parameters.
Preferably, the textile machine can be a carding machine.
It is further proposed that for setting the control parameters (control intensity) the quantity of the supplied fiber mass is varied by the carding machine for different measurement periods.
The speed of the feed roller to the carding machine can be constant and the speed of the doffer can be changed via the control unit.
It is similarly possible to change the speed of the feed roller to the carding machine via the control unit and to keep the speed of the doffer constant.
In both cases the carding machine will supply more or less fiber material to the downstream drafting arrangement unit following the change of speed. The effects of these different supply quantities with respect to the setting of the control parameters have already been described in the details on the method claims.
In order to adjust the measuring periods to the differently supplied fiber quantity, it is provided to use a timing element in order to consider the delay time between the start of the changed delivery quantity and the time at which the changed delivery quantity is processed in the drafting arrangement unit. The timing element can be considered within the scope of a software component in the control unit.
As has already been described above in closer detail, it is proposed that during the run-up of the carding machine a warm-up function for the machine is initiated in the control unit which cuts off certain means for monitoring and/or controlling.